Deflection circuit



Oct. 6, 1959 L. .1. KABELL ETAL DEFLECTION cmcun 2 Sheets-Sheet 1 Filed Aug. 4, 1958 WA 75065 SEA/67919704? (GU/5 J. 6644 7,946 0. JONES INVENTORS FIG-.1.

United States Patent Ofi ice 2,907,899 DEFLECTION CIRCUIT Louis J. Kabell and Earle D. Jones, Palo Alto, Calif., assignors to A. B. Dick Company This invention relates to circuits for producing voltages for cathode-ray tubes and, more particularly, to improvements therein.

'11. has been known that stable deflection of an electron beam from digital input information can be obtained by the use of precision direct-coupled amplifiers which are driven from accurate regulated current sources controlled by the digital input information. However, there is some basic instability in the direct-current amplifier due to changes in power supplies, components aging, and the like. To further stabilize such circuitry, very complex feedback arrangements are provided, and, further, well-regulated voltage sources are provided with precision components for the purpose of providing constant currents. Such arrangements me complex and expensive. Further, the stability obtained is limited to the quality of the voltage source, the accuracy of the precision components supplied, and primarily by the performance of the direct-current amplifier.

An object of this invention is to provide a simple circuit arrangement for producing deflection voltages for cathode-ray tube beam deflection.

Another object of the present invention is the provision of an inexpensive circuit arrangement for producing stable deflection voltages in response to digital input signals for deflecting the cathode-ray beam.

Yet another object of the present invention is the provision of a novel circuit arrangement which can produce stable deflection voltages for a cathode-ray oscilloscope.

These and other objects of the invention are achieved in an arrangement wherein a first and second series string of diodes are connected to a first and second constantcurrent source. To opposite deflection plates of the cathode-ray tube to which the voltages are to be applied are respectively connected between a constant-current source and the series string of diodes. There is provided a switch for each diode which is connected to bridge each diode. The diodes are all connected to the constantcurrent sources with a polarity so that a sufiicient current flow in the back direction develops the characteristic back voltage drop of a diode. When a switch is closed it bypasses the current around its associated diode, thus eliminating the back voltage drop of that diode. When a switch is opened, the current flows through the associated diode, establishing the back voltage drop thereacross.

Transistors are preferred as switches, and each one is accordingly connected across a diode to bypass current around it when rendered conductive. Each diode in the first series string of diodes has an associated diode in the second series string of diodes. Means are provided whereby it is possible to apply a pulse simultaneously to a transistor coupled across one of the diodes in the first diode string and to a transistor coupled across the associated one of the diodes in the second transistor string to change their states of conduction. Thereby, the back voltage drops of diodes in the first and second series 2,907,899 Patented Oct. 6, 1959 strings may be applied or removed to establish desired values of deflection voltages on the cathode-ray tube deflection plates.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings in which:

I Figure l is a circuit diagram of one embodiment of the invention; and

' Figure 2 is a circuit of the invention.

' An arrangement is shown for providing deflection voltages in response to signals on six input channels so that the cathode-ray tube beam may be positioned to one of 64 positions on an 8 x 8 matrix (zero signal input being considered as one input). Three of the six channels are decoded to determine one of eight horizontal deflection positions. A circuit for this is shown in detail. The remaining three channels are decoded to give one of eight vertical deflection positions. This requires identical circuitry with that shown for the horizontal deflection voltage generator and therefore is shown in block diagram form for simplicity.

The actual deflection voltages are developed across voltage reference diodes which are switched in or out of the deflection circuit by transistors according to the digital input information. These are diodes of the type which develop a Zener, or avalanche, effect when a voltage is applied across them with a reverse polarity. Referring to Figure 1, a circuit diagram of an embodiment of this invention is shown in which there are provided two constant current sources l0, 12. These comprise pentode tubes, respectively having cathode bias resistors 14, 16, and having their grids returned to ground through resistors 18, 24). The screen grids are connected to a source of grid potential through resistors 22 and 24. As a result, the pentode tubes 10, 12 are maintained conductive. In a preferred embodiment of the invention, these tubes were biased to provide a direct current of five milliamperes to their associate networks. The associated networks for the tube 10 includes a first series diode string having reference diodes 3d, 32, 34. These are connected in series, anode to cathode, and backwards between a source of positive potential and through a potentiometer 36 to the anode of tube 10. A sutficient current flow through a diode is provided to develop its characteristic back voltage drop. A compensating capacitor 38 is connected between one end of the potentiometer and the anode of tube 10. The other end of potentiometer 36 is connected to 13+ through a resistor 39.

A transistor is provided for each one of the diodes 30, 32, 34 in the series string. Each one of these transistors 40, 42, 44 has its emitter connected to the cathode of the diode with which it is associated and its collector connected to the anode of the diode with which it is associated. The emitter of transistor 40, as a result, is also connected to the source of B+, and the collector of the transistor 44 is connected to one end of the potentiometer 36.

A second series string of reference diodes 3t), 32, 34' is provided, each one of which is associated with and has substantially identical characteristics as the corresponding diodes 30, 32, 34 in the first series string. These diodes are connected in like manner between the B+ source and the plate of tube 12 through a potentiometer 36'. These diodes also develop their characteristic back voltage drop when a sufficient current flows through them. The other end of the potentiometer 36' is connected to B+ through a resistor 39'. A compensating diagram of a second embodiment the transistor 34,

' sistor i i then flowed through diode 34.

capacitor 38' is also connected between the other end o the potentiometer 3:6 and the anode of tube 12. Transistors 4t), 42' and 44 respectively have their emitters and collectors connected to the cathode and anode of the associated diodes 3%, 32' and 34'. As a result, the emitter of transistor an is connected to 13+ and the collectors of transistor 44 are connected to the potentiometer 36.

The arrangement employed for the transistors is such that in the quiescent state, the transistors associated with the first series string of diodes are not conducting, and a constant current flows through the reference voltage diodes, and develops their characteristic back voltages. In an embodiment of the invention which was built, these characteristic back voltages were respectively 10 volts for diode 20 volts for diode 32, and 40 volts for diode 30. In the quiescent state, the transistors 41), 4-2, and 44 are biased to conduct heavily with the result that no reference current flows through the reference diode 30, 32, and 3d. The circuit arrangements for obtaining nonconduction for the transistors 40, d2, 44, as shown in the drawing, comprise a resistor d, which connects the base of transistor 40 to one side of the first secondary winding 56 of a transformer 52. The other side of the secondary winding 56 is connected to the emitter of the transistor 4%. In the absence of any input signal being applied to the transformer 52, the emitter and base of the transistor 4% are essentially at the same potential, and therefore the transistor is cut oil. Transistors 42 and 44 are similarly connected respectively to the secondary windings 66 and '76 of the transformers 62 and 72, with the base being connected through a resistor 69, '76, respectively, and the emitters through direct connection.

A third winding d3, '78, for each one of the transformers, respectively '52, d2, 72, is provided for applying signals to the transistors 4h, 42', 44', respectively. The respective emitters of transistors 4d, 42, and 44- are respectively coupled through parallel connected resistors 57, 67', 77', and condensers 59, 69', and '79 to one side of the windings 58. The bases of the respective transistors dd, 42, and 4d are directly connected to the other side of the respective windings 53, 63, and '78. A source of negative bias potential is coupled to each one of the bases of these transistors through respective resistors 61, 71, and S1. The value of the negative po tential employed is such as to insure that the transistors 40', 42, and 44' in the quiescent condition are conducting heavily.

The sense of the coupling of the windings of the transformers is such that signals from the source of digital input signals 82, which are applied to any one or combination of primary windings 54, 64, 74' will render the transistors 46 42, 44 (which are coupled to the transformers receiving a pulse) highly conducting, while the associated transistors 4d, 42', 44' (coupled to the transformers to which the pulse is applied) are cut oil. In an embodiment of the invention which was built in the quiescent condition, the left one of the pair of deflecting electrodes 84 was at a potential of 13+ 70 volts, and the right one of this pair of deflection electrodes was at a potential of B-l- 0 volts. A pulse applied to the transformer 72 from the source of digital input signals rendered transistor 44 conductive, as a result of which the current which flowed through diodes 30 and 32 did not flow through diode 34, but was bypassed through the transistor 34. This eliminated the back voltage drop of which, as previously indicated, was a lO-volt drop. As a result, the potential applied to the left deflector oi the pair 84 rose from 13+ -7() volts toB-l- --6() volts. The transistor 4-4 was cut oil as a result of the applied pulse to the transformer 74. Eileetivcly, therefore, the current which flowed through tran- This caused a voltage drop of volts, and the potential applied to the right deflector 84, as a result,.became B+ -l0 put signals 82 provides the 1 volts. It should therefore be appreciated that by the application of the pulse to the transformer 72, the cathode-ray beam receives a deflection potential of 20 volts. The second pair of deflectors 86, which are in a cathode-ray tube, may be driven from a deflection voltage generator 88, which includes the circuitry just described for drivingthe deflectors 84. The source of digital indigital signals for driving the deflection voltage generator 88, as well as the one for which the circuitry is shown. It should be appreciated, therefore, that any combination of six binary digital signals may be applied to the two deflection voltage gen.

erators for positioning a cathode-ray beam in one of 64 positions. The fact that an arrangement has been shown and described for handling six binary digital should not be construed as a limitation, since those skilled in the art from the teachings made herein will readily appreciate how this invention may be extended for handling other numbers of digital input signals.

Reference is now made to Figure 2 of the drawings, which is a circuit diagram of another embodiment of the invention. The arrangement shown in Figure 2 is one wherein all the transistors 1%, H2104, 109', 102', and 104' are connected to be nonconductive in the quiescent condition and to be made conductive in associated pairs Mill-109, 1tl2-1h2', 1tl41tl4' upon the application of a pulse to the primary windings of transformers 120, 122, 124. The series diode string 110, 112, 114 is connected between a 3+ source and a constant currentgenorator with a polarity so that the. potential at the-left deflector 84 of a cathode-ray tube will become more positive when current is bypassed around one of the diodes, removing its back voltage drop from the active element potential ladder to which this deflector is con- 7 nected.

The diodes lit), 112', 114 of the second series string are connected between ground and a constant current generator with a polarity so that the potential of the right deflector 84 of the cathode-ray tube will become less positive when current is bypassed around one of these diodes, removing its back voltage drop from the active element potential ladder to which this deflector is connected.

' The transistor Hill has its emitter connected to 13+, to the cathode of diode 116, and to one end of one secondary winding 1203 of transformer 1'20. The base of transistor 160 is connected through a resistor 101 to the other side of secondary winding 12493. The collector of transistor ltitl is connected to the emitter of transistor 102, to the anode of diode 110, to the cathode of diode 112, and to one end of secondary winding 122B. The base of transistor 1&2 is connected through a resistor 1 03 to the other end of secondary winding 1223. The emitter of transistor 104 is connected to the collector of transistor 102, to the anode of diode 1112, to the cathode of diode 114, and to one end of secondary winding 12413. The base of transistor 104 is connected through a resistor 195 to the other end of secondary winding 124B.

The collector of transistor 104 is connected to the anode of diode 104, a deflection plate 84, and to the constant current generator. transistor 130, having its collector connected to the collector of transistor 1M its base connected to B+ through a limiting resistor 132, and its emitter connected through a resistor 136 to ground. A diode has its anode connected to ground and its cathode connected to the base of transistor i130. The diode 138 is connected so that a back voltage drop is developedacross it which serves to bias transistor 130 to be conductive. 1

Transistor 106' has its collector connected to ground and to the anode of diode 116*. The base of transistor 109' is connected through resistor 1'01 to one end of secondary winding 120C. The emitter of transistor is connected to the other end of secondary winding 120C,

to, the cathode of diode to the. anode of diode 1 41,21,.

input signals This includes an IJPN-type and to the collector of transistor 102'. The base of transistor 102 is connected through a resistor 103' to one end of secondary winding 122C. The emitter of transistor 102 is connected to the cathode of diode 112, to the anode of diode 114', to the collector of transistor 104', and to the other end of secondary winding 122C. The base of transistor 104 is connected through a resistor 105' to one end of a secondary winding 124C.

The emitter of transistor 164' is connected to the other end of secondary winding 124C, to the cathode of diode 114', to the other deflector 84, and to a second constant current generator. This includes a PNP-type transistor 140 having its collector connected to the emitter of transistor 104, its base connected through a resistor 142 to ground, and its emitter connected through a limiting resistor 146 to 13+. A diode 148 is connected with reverse polarity between base and B+ so that its constant back voltage drop can be obtained and used for biasing the transistor 140 to be conductive. The source of digital input signals 82 and the deflection voltage generator 88 perform the same functions and represent the same structure as represented in Figure 1.

From the connections for the transistors described for Figure 2, it will be seen that in the quiescent state their bases and emitters are essentially at the same potentials, and they are therefore in a substantially nonconductive state. Therefore, current flows through the first diode series string which is interposed between the highest potential point or B+ and the left deflection plate 84. Current flows through the second diode series string which is interposed between the lowest potential point or ground and the right deflection plate 84. The application of a pulse to the primary windings of one or more of the transformers can make the bases of the transistors sufliciently negative to render them conductive. Thereby, the back voltage drops of the associated diodes in the first and second series strings are removed, bringing the left deflection plate closer to the highest potential and the right deflection plate closer to ground potential.

Accordingly, there has been described and shown a new and novel arrangement for synthesizing deflection voltages from digital input signals to accurately position an electron beam of a cathode-ray tube. The deflection voltages presented are stable for the reason that the voltage reference diodes which are employed are essentially a constant voltage, low-incremental impedance device, which are driven from an essentially constant current source. The characteristic reference voltages for the diodes are chosen to be near the zero temperature coeflicient point of operation for these diodes, thus further assuring stability.

We claim:

1. A circuit for producing stable voltages in response to digital input signals comprising a first and second plurality of diodes each having an anode and cathode, means connecting said first plurality of diodes in a first series string with the anode of one diode being connected to the cathode of another diode, means connecting said second plurality of diodes in a second series string with the anode of one diode being connected to the cathode of another diode, a first and second plurality of switch means, means for connecting each of said first plurality of switch means in parallel with a different one of said first plurality of diodes, means for connecting each of said second plurality of switch means in parallel with a different one of said second plurality of diodes, a first constant current source, a second constant current source, means for connecting said first series string to said first constant current source to develop the characteristic back voltages of said first plurality of diodes upon current flow therethrough, means for connecting said second series string to said second constant current source to develop the characteristic back voltages of said second plurality of diodes upon current flow therethrough, means for selectively and simultaneously operating said first and second switch means responsive to said digital input signals, and means to derive output voltages from the respective connections between said first and second constant current sources and said first and second series strings.

2. A circuit as recited in claim 1 wherein said first and second constant current sources respectively comprise a transistor, and means for biasing said transistor for conduction with a constant bias; and each said first and second pluralities of switch means includes a transistor, and means for controlling the conductive state of each transistor in response to said digital input signals.

3. A circuit as recited in claim 1 wherein said first and second constant current sources respectively comprise tubes, and means for biasing said tubes for conduction with constant'current; and each said first and second plurality of switch means includes a transistor, and means for controlling the conductive state of each transistor in response to said digital input signals.

4-. A circuit for producing stable voltages in response to digital input signals comprising a first and second plurality of diodes each having an anode and cathode, means connecting said first plurality of diodes in a first series string with the anode of one diode being connected to the cathode of another diode, means connecting said second plurality of diodes in a second series string with the anode of one diode being connected to the cathode of another diode, a first and second plurality of transistors each transistor having base, emitter and collector elements, means for connecting the emitter and collector of each transistor in said first plurality of transistors to the respective cathode and anode of a different diode in said first plurality of diodes, means for connecting the emitter and collector of each transistor in said second plurality of transistors to the respective cathode and anode of a different diode in said second plurality of diodes, a first and second constant current source, means for connecting said first series string to said first constant current source to develop the characteristic back voltages of said first plurality of diodes upon current flow therethrough, means for connecting said second series string to said second constant current source to develop the characteristic back voltages of said second plurality of diodes upon current flow therethrough, means for selectively and simultaneously applying said digital input signals between the emitter and base of transistors in said first and second pluralities of transistors to control the conductive state of said transistors in response to said digital input signals, and means to derive output voltages from the respective connections between said first and second constant current sources and said first and second series strings.

5. A circuit for producing stable voltages as recited in claim 4 wherein said means for selectively and simultaneously applying said digital input signals between the emitter and base transistors in said first and second pluralities of transistors to control the conductive state of said transistors in response to said digital input signals includes a plurality of transformers each having a primary winding and a first and second secondary winding, means coupling each said first secondary winding between the emitter and base of a different one of said first plurality of transistors, means for coupling each said second secondary winding between the emitter and base of a different one of said second plurality of transistors, and means for applying said digital input signals to said primary windings.

6. A circuit for producing stable voltages as recited in claim 5 wherein said first constant current source includes an NPN-type transistor, having a collector connected to said first series string, a base, and an emitter, and means for applying a constant bias to said base including a resistor and a diode connected to said resistor to provide its characteristic back voltage upon current flow therethrough; said second constant current source cluding a resistor and a diode connected to said resistor to provide its characteristic back voltage upon current flow therethrough.

7..A circuit for producing stable deflection voltages in response to digital input signals comprising a first plurality of diodes, a second plurality of diodes, each of said second plurality of diodes being associated with a difierent one of the diodes in said first plurality of diodes, a first and second constant current source, means for connecting said first and second pluralities .of diodes respectively in series strings and to said first and second constant current sources to develop the characteristic back voltages of said diodes upon current :fiow there through, a plurality of normally open switch means each of which is connected in parallel with a diflferent one of the diodes in said first plurality of diodes, a plurality of normally closed switch means each of which is connected in parallel with a different one of the diodes in said second plurality of diodes, means for selectively applying digital signals simultaneously to a normally open and normally closed switch means coupled to associated diodes in said first and second plurality of diodes to close a normally open switch means and to open a normally closed switch means, and means to derive an output from the connections between said first and second sources of constant current and said first and second pluralities of diodes. a '8. A circuit as recited in claim 7 wherein said first and second constant current sources are tubes, and means for biasing said tubes for constant current conduction; each said normally open switch means includes a transistor, and means biasing said transistor to be nonconductive; and each. said normally closed switch means includes a transistor, and means biasing said transistor to be conductive. V

9. A circuit for producing stable deflection voltages in response to digital input signals comprising a first plurality of diodes, a second plurality of diodes each of which is associated with a different one of said first plurality of diodes, a first and second constant current source, means for coupling said first and second pluralities of diodes in series strings respectively to said first and secndv constant current sources to develop the characteristic back voltages of said diodes upon current flow therethrough a diiferent transistor for and associated with each diode in said first and second pluralities of diodes, each said transistor having a base, emitter and collector element, means connecting each diode to the emitter and collector of its associated transistor, means for biasing the transistors connected to said first plurality of diodes to be nonconductive, means for biasing the transistors connected to said second plurality of diodes to be conductive, means for applying digital input signals selectively and simultaneously to the transistors connected to associated diodes in said first and second pluralities of diodes for rendering conductive the nonconductive transistor and rendering nonconductive the conductive transistor, and means for derivin an output from the connections between said first and second sources of constant current and said first and second pluralities of diodes.

1.0. A circuit for producing stable deflection voltages in response to digital input signals comprising a first plurality of diodes, a second plurality of diodes each of which ing a base, emitter and collector element, means connecting each diode to the emitter and collector of its associated transistor, a plurality of transformers each having an input and a first and second output Winding means coupling each one of said first output windings between the base and emitter of a difierent one of said transistors associated with said first plurality of diodes, means coupling each one of'said second output windings between the base and emitter of a different one of said transistors associated with said second plurality of diodes, means to apply a bias toeach of said transistors associated with said second plurality of diodes to render each of them conductive, means for applying digital inputsignals to desired ones of said transformer input windings to respectively render conductive and nonconductive transistors connected to their first and second output windings, and means to derive an-output fromthe connections between said first and second source of constant current.

11. A circuit for producing stable deflection voltages in response to digital input signals comprising a first plurality of diodes, a second plurality of diodes each of said second plurality of diodes being associated with one of said first plurality of diodes, a first and second plurality of transistors respectively associated with said first and second plurality of diodes each transistor having an emitter, collector and base element, means connecting each diode across the emitter and collector of an associated transistor in a nonconductive direction, a first and second tube, a first and second load resistor respectively connected to said first and second tubes, means respectively connecting said first and second pluralities of diodes across said first and second load resistors, a plurality of transformers each having an input and a first and second output winding, means coupling each one of said first output windings between the base and emitter of a different one of said transistors associated with said first plurality of diodes, means coupling each one of said second output is associated with a different one of said first plurality of windings between the base and emitter of a different one of said transistors associated with said second plurality of diodes, means to apply a bias to each of said transistors associated with said second plurality of diodes to render each of them conductive, means for applying digital input signals to desired ones of said transformer input windings to respectively render conductive and nonconductive transistors connected to their first and second output'windings, and means to derive an output from the connections between said first and second source of constant current.

12. A circuit for producing stable deflection voltages in response to digital input signals comprising a plurality of transformers each having an input winding to which digital input signals are applied and a first and second output winding, a first and second plurality of transistors each having a base, emitter and collector element, means coupling the base and emitter of each of said first plurality of transistors to a different one of said first output windings, means coupling the base and emitter of each of said second plurality of transistors to a different one of said second output windings, means biasing the transistors in said second plurality .to be conductive, a separate diodefor each transistor, means coupling each diode across the emitter and collector of a. transistor in a non conductive manner, means connecting said diodes connected to said first plurality of transistors in, a first series string, means connecting said diodes connected to said second plurality of transistors in a second series string, a first tube connected to said first series string of diodes, a second tube connected to said second series string of diodes, means for applying operating potential to said re: spective tubes across said respective first and second diode series strings, and means to derive an output from the connections between said first and second series diode strings and saidfirst and second tubes. 7

:No references cited. 

